1. Field of the Invention
The present invention relates to a back illuminated photodiode array, the manufacturing method and semiconductor device such as a radiation detector provided with back illuminated photodiode arrays.
2. Related Background Art
A CT (computed tomography) device is provided with a plurality of back illuminated photodiode arrays. A back illuminated photodiode array can be increased in the density per unit area when an electronic circuit for the back illuminated photodiode array is placed in an extended thickness direction of a semiconductor substrate in arranging a plurality of back illuminated photodiode arrays.
More particularly, when back illuminated photodiode arrays for CT are mounted, they must be mounted in a three dimensional manner. Thus, in mounting the arrays in a three dimensional manner, an output signal must be output from the surface opposite to the light-incident surface.
A back illuminated photodiode array is provided with a semiconductor substrate having a back surface acting as a light-incident surface, a plurality of pn junctions formed inside the semiconductor substrate and an electrode formed on the front surface of the semiconductor substrate.
Carriers generated inside the semiconductor substrate move toward each pn junction and is taken out through the electrode. In this instance, where a distance is great between each pn junction and the light-incident surface, a carriers generated inside the semiconductor substrate undergo recombination during a transferring process to the pn junction and cannot be taken out as a signal. Therefore, it is preferable to maintain as small as possible a distance between the pn junction and the light-incident surface.
FIG. 42 is a schematic view showing the cross sectional configuration of a conventional back illuminated photodiode array.
The back illuminated photodiode array has been described, for example, in Japanese Unexamined Patent Publication No. 7-333348. This back illuminated photodiode array is provided with a rectangular column-shaped p-type diffusion region 105 formed inside an n-type semiconductor substrate, and a p-type diffusion region 105 extends in the direction from the front surface of the semiconductor substrate to the back surface. Therefore, a boundary surface (pn junction) with the p-type diffusion region 105 and n-type layer 103 is closer to the back surface (light-incident surface) of the semiconductor substrate, thereby making smaller the distance between the light-incident surface and the pn junction.